This invention relates to absorption refrigeration and, in particular to a dilution cycle for use in an absorption chiller.
Dilution cycles are run in absorption chillers to lower the refrigerant concentration in the absorbent solution so that the solution does not crystallize as the solution temperature approaches the ambient temperature. The lower the solution concentration, the lower the solution temperature can be at shut down without having to be concerned with crystallization. However, the lower the solution concentration at shut down, the longer it will take to reconcentrate the solution to an operating level at start up.
For example, in many chillers in present day use the dilution cycle is accomplished by first shutting down the heater used to raise the temperature in the upper or high temperature stage generator of the machine. The solution and refrigerant pumps as well as the chilled water and condenser water pumps, however, are allowed to continue to run for a given predetermined period time after the heat to the generator is terminated. The preset time interval generally must be relatively long in order to dilute highly concentration solution in the event the machine is operating under full load at the time of shut down. Correspondingly, when the machine is shut down when operating under a partial load, the preset time period allows the solution to become overly diluted thus requiring a relatively long time to reconstitute the solution at start up. As can be seen, the use of a predetermined dilution time cycle can cause the machine to run longer than necessary at shut down or can extend the time necessary to reconcentrate the solution when the chiller is restarted. In either case, this type of dilution cycle can cause a good deal of energy to be wasted during both shut down and start up.
It is a primary object of the present invention to improve dilution cycles used in absorption chillers.
It is a further object of the present invention to save energy during the shut down and restarting of an absorption machine.
Another object of the present invention is to provide a dilution cycle control that is able to determine how long the cycle must run at shut down in order to safely shut down the machine.
A still further object of the present invention is to control the dilution cycle of an absorption chiller in response to the crystallization temperature of the solution and the ambient temperature at shut down.
Yet another object of the present invention is to provide a highly efficient dilution cycle for use in an absorption chiller that employs a versatile shut down routine that is suitable for use regardless of the cause of the machines shut down.
These and other objects of the present invention are attained by a routine for controlling the dilution cycle of an absorption chiller that determines when the dilution cycle is to be initiated, continued and terminated. The concentration of solution leaving the low temperature generator of the chiller is first calculated and from this calculation the crystallization temperature of the solution is determined. The crystallization temperature is compared to the ambient temperature surrounding the chiller and, based upon the comparison, a determination is made whether to initiate a dilution cycle or to continue the cycle once it has started, and lastly when to terminate the cycle in order to conserve energy without endangering the chiller.